High thermoelectric and mechanical performance in the n-type polycrystalline SnSe incorporated with multi-walled carbon nanotubes

In this study, we introduce multi-walled carbon nanotubes (MWCNTs) in Pb/I co-doped n-type polycrystal SnSe to simultaneously improve its thermoelectric and mechanical properties for the first time. The introduced MWCNTs act as the “bridges” to accelerate the electron carrier transport between SnSe grains, leading to significantly increased electrical conductivity from 32.6 to 45.7 S cm⁻¹ at 773 K, which contributes to an enhanced power factor of ∼5.0 μW cm⁻¹ K ^{− 2} at this temperature. Although MWCNTs possess high intrinsic thermal conductivities, these MWCNTs, acting as nanoinclusions in the SnSe matrix to form the dense interfaces between SnSe and MWCNTs, provide extra heat-carrying phonon scattering centers, leading to a slightly reduced lattice thermal conductivity of only 0.34 W m ^{− 1} K ^{− 2} at 773 K and in turn, a high ZT of ∼1.0 at this temperature. Furthermore, the introduced MWCNTs can simultaneously act as the “binders” to bond adjacent grains, significantly improving the mechanical properties of SnSe by boosting its Vickers hardness from 39.5 to 50.5. This work indicates that our facile approach can achieve high thermoelectric and mechanical properties in n-type SnSe polycrystals with a considerable potential for applying to thermoelectric devices as n-type elements.